Electric generators have been known for some time. Their action is based on the conversion of kinetic energy or mechanical energy into electric energy, wherein as a result of movement of an electric conductor in a magnetic field a voltage is induced in the conductor. The triumph of electrification was only able to be made possible and to enter into our daily routine with the development of electric generators.
For the generation of electric energy, large electric power station generators are used today. On account of power losses during their operation as a result of eddy-current losses, magnetization losses due to hysteresis, or friction losses caused by bearings and seals, etc., considerable heating of the electric generator occurs and has a negative influence on its power efficiency and therefore on its economic efficiency.
For this reason, a power loss occurring in the form of heat has to be dissipated because the electric generator can otherwise overheat. Cooling of electric generators is particularly desirable due to this.
However, the previous concepts for the cooling of electric generators offer still more potential for improvement. For example, power station generators up to an output of 300 MW are cooled by means of a forced cooling system. In the case of electric generators of this performance class this type of cooling reaches a physical limit since an air velocity which is required for the cooling of the electric generator is so high that a cooling effect is neutralized as a result of friction losses of the air in the electric generator. Considerations for improving the cooling effect make very high demands on the geometry of the electric generator. A disadvantage of this method is that parts of the electric generator which for example are located in the middle of the electric generator are insufficiently cooled.
In contrast, most electric generators with an output of from about 300 MW onwards are usually liquid cooled. Liquid cooled electric generators with such a high output no longer have stator windings but require stator bars. A cooling fluid then flows through the stator bars, absorbing or dissipating the lost heat.
In further considerations, attempts were made to install a thermosiphon cooling system in an electric generator. This cooling method, however, has the disadvantage that the way in which a cooling fluid is distributed in the individual stator bars cannot be actively influenced.